Presentation on theme: "Rietveld Refinement. Why do Reitveld Refinement?"— Presentation transcript:
Why do Reitveld Refinement?
What are the limitations of Rietveld? Phase detection limit of 1-5% Impurity atom determination New/unknown crystal structures Determination of disorder parameter Multiple parameters can have same effect diffraction patterns Equipment (powder vs. single crystal, x-rays vs. neutrons) Garbage in, garbage out! (noisy data, poor quality sample, poor sample prep)
Some common challenges/problems False minimas Refinement diverges (“blows up”) Which goodness of fit to choose? R vs. Chi sq? Preferred orientation Large amorphous background Incorrect starting crystal structure or lattice parameter Poor quality data!
Resources and links GSAS/EXPGUI: html html GSAS tutorials: _Crystallography/ _Crystallography/ FullProf: https://www.ill.eu/sites/fullprof/https://www.ill.eu/sites/fullprof/ PowDLL (file conversion): Lots of info about fitting parameters: ements.pdf ements.pdf People: Lauryn Baranowski Lakshmi Krishna